A control channel carries downlink control information. The downlink control information may be used to carry control channel command information. For example, the control channel command information may include one or more of a random access preamble index indication, a random access channel profile index indication, or a random access channel coverage enhancement level indication.
The downlink control information may further be used to carry grant information. The grant information carries control information required by user equipment to receive or send data. Downlink control information used to indicate downlink data transmission may be referred to as downlink grant. Downlink control information used to indicate uplink data transmission may be referred to as uplink grant.
In order not to increase control channel blind detections performed by user equipment (UE), a payload (payload) size (for example, a quantity of bits) of a control channel carrying grant information is usually the same as a payload size (for example, a quantity of bits) of the control channel carrying control channel command information. Therefore, it is necessary to differentiate whether downlink control information carries the grant information or the control channel command information for the UE.
In the prior art, when the downlink control information carries the control channel command information, there are usually many spare bits. The spare bits may be reserved bits or padding bits. The spare bits may also be difference bits between all bits included in a meaningful field when the downlink control information carries the grant information and all bits included in a meaningful field when the downlink control information carries the control channel command information. The meaningful field indicates that the field has a definite physical meaning in the downlink control information. The meaningful field is not a reserved bit, a padding bit, or a spare bit. Functions borne by the downlink control information can be differentiated by setting the spare bits to preset values. For example, if the downlink control information carries the control channel command information, there are 30 spare bits. A state of the 30 spare bits may be set to a fixed bit state. In this way, when the downlink control information carries the grant information, a bit state corresponding to the 30 spare bits in the downlink control information is not the foregoing fixed bit state. Because there are many spare bits, when the downlink control information carries the grant information, a base station is sufficiently capable of flexibly setting the bit state corresponding to the spare bits in the downlink control information to a state other than the fixed bit state. In this way, whether the downlink control information carries the grant information or the control channel command information can be differentiated according to the bit state corresponding to the spare bits.
However, in a coverage enhancement scenario, there are few bits in downlink control information. When the downlink control information carries the control channel command information, there are only a few spare bits (for example, only one spare bit). There is a high probability that functions borne by the downlink control information cannot be differentiated by setting the spare bits to preset values. For example, if the downlink control information carries the control channel command information, there is one spare bit. According to the prior art, a bit state corresponding to the one spare bit may be set to a fixed bit state. When the downlink control information carries the grant information, there is a high probability that the bit state corresponding to the one spare bit is the foregoing fixed bit state. As a result, a probability of falsely determining, by the user equipment, content borne by the control channel is increased. That is, in the coverage enhancement scenario, whether the downlink control information carries the grant information or the control channel command information cannot be differentiated according to the bit state corresponding to the spare bit.